Dimple rudder skins and stiffeners.
Dimples are formed in the adjoined parts. This makes the rivet sit flush with skin, and also makes for a much stronger structure because the dimples nest together. It takes more effort, but the results are much better than just riveting with round head rivets. Most production aircraft use round heads. Less labor and cheaper to build.
From Dale's RV Project - Empennage |
From Dale's RV Project - Empennage |
Example of what a Cessna wing looks like (note the round head rivets).
From Dale's RV Project - Empennage |